1. Field of the Invention
The present invention relates to a wet etching method of semiconductor processing, and more particularly, to a method for wet etching of thin film by forming a puddle of etching solution on the wafer in a spin processor
2. Description of Relative Prior Art
In semiconductor processing, batch wet etching or spin etch by using a single wafer spin processor is usually used to etch different kinds of thin film such as silicon dioxide, silicon nitride, silicon oxynitride, poly silicon, metal film, metal-silicide film, etc. The batch method do not suitable to large diameter wafers, the single wafer spin etch is suitable to diameter above 8 inches. However, supplying etching solution to the spinning wafer will waste a lot of etching solution, the uniformity is not good enough, the reason is that the staying time of the etching solution on the center and on the periphery of the wafer is different.
Using dry etching has high value of equipment and special gas problem, and dry etching is not suitable if isotropic or selective etching is required. So it needs an etching method to eliminate the consumption of etching solution, to has high uniformity, and to increase the etch rate but still keep all the advantages of wet etching.
It is an object of the present invention to provide a single wafer wet etching method with increasing etch uniformity, the uniformity is better than supplying etching solution during the wafer is spinning at high speed.
Another object of the present invention is to provide a single wafer wet etching method with less etching solution consumption, as a large quantity of etching solution is cut down, it still keep the etching capability. The third object of the present invention is to provide a single wafer wet etching method with higher etching rate as compare to spin etching.
To achieve this and other advantages and in accordance with the purpose of the present invention, the present invention make use of a spray and spin etch processor to form a puddle of etch solution on the wafer or substrate and keep the wafer spin in a very low speed (for example 10 rpm), so that the etch solution will stay on the wafer uniformly but will not leaving the wafer and etching can be carried out, the etching solution will have sufficient time to contact with the thin film which is not protected by photo-resist or etch mask. After etching, the etch solution is then spin off with high speed, then spin rinsing with D.I. water. The etch rate is better than spin etch and the uniformity is also better.
The puddle etching method of the present invention comprising the following steps: (1) Put the wafer into a spin processor, then spin with 800-1200 rpm for 1 sec.;(2) Spin with 800-1200 rpm to pre-wet the wafer for 10-20 sec.;(3) Inject etching solution from the front side and back side rinse (BSR) with an injection rate of 600 cc/min and spin with 800-1200 rpm to remove the thin film on the surface of the wafer for 10-20 min;(4) Stop injection of etch solution, spin with 800-1200 rpm to remove the etching solution for 1 sec.;(5) Form puddle of etching solution by injected etching solution, in the present embodiment, silicon dioxide film is etched by using diluted HF (DHF, HF:H2O=1:100) solution, with flow rate of 0.6-5 l/min for 3 sec., which is depend on the size of the wafer, larger wafer need more solution, the spin speed of the wafer is kept in 0-50 rpm to keep the solution stay on the wafer, too fast may loose part of the solution, but without spin may result non-uniformity; (6) Keep the wafer spin with 0-50 rpm, the better is 15 rpm, to keep the solution not fry away from the wafer, but may not stop spinning, and should be spin slowly to keep the solution stay on the wafer uniformly to perform puddle etching, the etching time is depended on the thickness of the thin film; (7) Speed up to 800-1200 rpm, inject D.I. water from the front side and BSR to rinse for 20-25 sec.; (8) Stop supplying D.I. water on both the front side and BSR, pre-spin with 600-1000 rpm for 1 sec. to spin off the D.I. water; (9) Inject IPA, the speed is slowed down to 40-100 rpm for 1.5 sec. By using Marangoni effect to make the wafer more clean; (10) Speed up to 1000-2000 rpm for 2 sec. to pre-dry the wafer; (11) Speed up to 3000 rpm or more for 20 sec, to dry the wafer completely.